A fuel cell has been proposed as a clean, efficient and environmentally responsible power source for electric vehicles and various other applications. In particular, the fuel cell has been identified as a potential alternative for the traditional internal-combustion engine used in modern vehicles.
One type of fuel cell is known as a proton exchange membrane (PEM) fuel cell. The PEM fuel cell typically includes three basic components: a cathode, an anode and an electrolyte membrane. The cathode and anode typically include a finely divided catalyst, such as platinum, supported on carbon particles and mixed with an ionomer. The electrolyte membrane is sandwiched between the cathode and the anode layers to form a membrane-electrode-assembly (MEA). The MEA is often disposed between porous diffusion media (DM) which facilitate a delivery of gaseous reactants, typically hydrogen from a hydrogen source and oxygen from an air stream, for an electrochemical fuel cell reaction. In automotive applications, individual fuel cells are often stacked together in series to form a fuel cell stack having a voltage sufficient to power an electric vehicle. The DM's and MEA are pressed between a pair of electronically conductive plates which conduct current between adjacent cells internally of the stack in the case of bipolar plates and conduct current externally of the stack in the case of monopolar plates at the end of the stack.
The plates each contain at least one active region that distributes the gaseous reactants over major faces of the anode and cathode. These active regions, also known as flow fields, typically include a plurality of flow channels to supply the gaseous reactants to the electrodes on either side of the PEM from an intake manifold. In particular, the hydrogen flows through the channels to the anode where the catalyst promotes separation into protons and electrons. On the opposite side of the PEM, the oxygen flows through the channels to the cathode where the oxygen attracts the hydrogen protons through the PEM. The electrons are captured as useful energy through an external circuit and are combined with the protons and oxygen to produce water vapor at the cathode side.
The flow of reactants through the channels must be precise to maintain optimum performance of the fuel cell. The flows of the reactants are typically monitored by one or more pressure sensors in communication with the flow paths of the reactants. Inaccurate pressure measurements by the sensors can result in a low reactant pressure within the fuel cell. Low reactant pressure can lead to an insufficient supply of the reactants necessary to produce the desired electrical output. Alternatively, inaccurate pressure measurements can result in high reactant pressure that can cause other issues. Known pressure sensors are susceptible to such inaccurate measurements when the fuel cell is operating at a sub-zero temperature, or a temperature below the freezing point of water. Such temperatures may cause the water vapor within the fuel cell to condense and freeze. The frozen condensate can interfere with communication between the reactant flow path and the pressure sensor, resulting in inaccurate pressure measurements. Over time, the frozen condensate may also cause corrosion of the pressure sensor, reducing the useful life of the sensor.
It is desirable to produce a pressure sensor for a fuel cell system that optimizes a durability and an accuracy of the pressure sensor, particularly during operating conditions in which water within the fuel cell system freezes.